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September 2019

On thin ice

by Hendrik Thielemann

Our Arctic permafrost is melting, and this has serious adverse ­consequences for local habitats as well as for the global climate. ­Scientists from the German Aerospace Center (DLR) are therefore ­observing the permafrost region in northern Canada and taking ­measurements with highly advanced imaging radar while flying over the vast stretches of the Arctic Circle around 66° 33’N with a Dornier 228 aircraft. The melting of the Arctic’s permafrost is important, as scientists have found it causes erosion, leading to barren Arctic lands, the ­disappearance of lakes, landslides and ground subsidence changes which influence plant species compositions.

Almost a quarter of the land surface of the Earth’s northern hemisphere consists of ­permafrost, including large parts of Canada, Alaska and Siberia. Permafrost is soil that has been frozen for at least two years. It is found at high latitudes and in high mountains. Most of today’s permafrost can be dated back to the last Ice Age. To remain stable, it needs an annual average temperature of less than minus one degree Celsius.

On_thin_ice_Grafik_2 On thin ice

Source: Arctic Climate Impact Assessment (ACIA), 2004 Impacts of Warming Arctic

Rising temperatures worldwide have led to permafrost soils slowly thawing in many regions, causing damage to local ecosystems, changing the range of habitat for temperate species and increasing the successful growth of pest species. The thawing of permafrost also allows more water to seep through the soil, bringing about the disappearance of lakes and wetlands. As the perma­frost ice melts, soil becomes weak and unstable, which contributes to coastal erosion. In mountainous areas, the risks of landslides and rockfalls increase. The change in the earth’s surface structure also affects village communities and economies, forcing families to move and costing billions in repairs and resettlement.

Huge quantities of greenhouse gases could be released

The ramifications of melting permafrost for the global climate are even more dramatic. During and since the last Ice Age, organic animal and plant remains were stored in soils and sediments and sealed in permafrost like in a gigantic freezer. If the permafrost thaws, microorganisms can decompose the carbon-containing organic material. This decomposition process releases the greenhouse gases carbon dioxide and methane into the atmosphere. The result: global warming is accelerated – and with it the degradation of more permafrost. This can lead to a dangerous and irreversible vicious circle known as “permafrost-carbon feedback.” Scientists estimate that around 1,500 gigatons of carbon are stored in permafrost – twice as much as is currently stored in the Earth’s atmosphere.

The investigation

Scientists from the German Aerospace Center (DLR) and their colleagues from the Canada Centre for Mapping and Earth Observation (CCMEO) closely investigated the permafrost region in northern Canada in order to better understand the effects global warming had on local permafrost. The researchers developed special radar technologies and analytical methods to aid in developing a highly accurate observation technique. Measurement flights were conducted in a Dornier 228-212, which played a key role in this project. Its robust design, innovative imaging radar system and numerous other modifications made it ideally suited for remote sensing missions.

In August 2018 the DLR Microwaves and Radar Institute conducted their first measurement flights from the Inuvik and Yellowknife base stations in the ­Canadian Northwest Territories. The scientists flew through ten test areas from northern Saskatchewan to the ­Canadian Arctic coast to record the state of permafrost in late summer. In order to gain an insight into the completely frozen state of the permafrost regions, the research team then conducted a second measurement campaign in the same areas in the spring of 2019. ­Taking measurements during two different seasons helps scientists observe and characterize changes more accurately.

On_thin_ice_Grafik_1 On thin ice

Seeing below the Earth’s surface

DLR’s Dornier 228 is equipped with a special radar system that can transmit radar beams from the air to the ground in four different wavelengths. “For us, the Dornier 228’s exploration flights were primarily about testing innovative radar technologies,” explains Irena Hajnsek, Science Coordinator of the German Radar Satellite mission TanDEM-X at DLR. Researchers at DLR are particularly interested in synthetic aperture radar (SAR) tomography, a method in which long-wave radar beams make it possible to look beneath the Earth’s surface and produce a three-dimensional image of its layers.

“SAR tomography enables us to look deep into the ground,” explains radar expert Hajnsek. And what the researchers see gives us cause for concern: According to Irena Hajnsek, the permafrost line is moving further and further north. SAR tomography can also provide insights into the damage caused by the thawing of the permafrost – especially the erosion that occurs when the soil is no longer held together by the eternal ice. “North of Inuvik, for example, there are large areas where the sandy soil is completely eroded,” reports Hajnsek.

On_thin_ice_1 On thin ice

The DLR’s Dornier 228-212 research aircraft. (Photo: DLR / Helmut Kirner)

When the soil is completely frozen the radar waves can “penetrate depths up to several meters – but only then. In cases where the soil surface is not completely frozen, due to seasonal temperature changes, surface indicators are used to gain information about the permafrost change,” explains Hajnsek. She cites vegetation as an example: Certain plants, such as birches, do not grow on permafrost soils. If we observe birch growth in certain regions, we can conclude that the permafrost is thawing in deeper soil layers. Some plants can even be invasive, causing shifts in the animals and insects that thrive on those plants, and new species in a territory can have repercussions on those already living there.

Now that the flights in northern Canada have been completed, Irena Hajnsek and the DLR researchers are working on further developing their radar technology and algorithms with the help of the data collected. The radar instrument on board the Dornier 228 is to pave the way for the future use of SAR tomography in space. DLR is planning an Earth observation mission consisting of two satellites, called Tandem-L. These two radar satellites will study the dynamic processes at and below the Earth’s surface on a global scale at a hitherto unknown quality. Collecting this amount of targeted data will help scientists observe the development and destruction of the fragile ecosystem of the Arctic so that we understand how our thinning ice is affecting our planet and can perhaps find a way to reverse it or at least slow it down until the next Ice Age.

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Flying research platform for Earth observation. (Photo: DLR / Helmut Kirner)

DLR’s Dornier fleet

The German Aerospace Center operates two different versions of the Dornier 228.

The first Dornier Do 228-101 is based at Braunschweig in northern Germany and is used as a flying research platform for various experiments. Aerodynamic research, such as laminar wing development, enhanced vision, flight guidance and optional piloted vehicle development are daily routine for the highly sophisticated aircraft.

The second Dornier 228-212 is based at the Oberpfaffenhofen facility near Munich. Its main role is to accommodate teams that need remote sensing applications. The aircraft is also built in such a way that a large variety of instruments can be installed, which is a plus for research teams. For the permafrost measurements in northern Canada, for example, the Dornier 228 was equipped with DLR’s F-SAR radar system.

Both 228s are specially modified for use as research aircraft. External stores for pods and antennas as well as camera floor openings and roof aperture plates are installed to fit any researcher’s needs. Together with various navigation systems and avionics such as a flight management system, TCAS and TAWS make both aircraft compliant with modern operational requirements all over the world. An additional power supply system is available in the cabin to power the scientific payload.

A pilot’s perspective

Captain Helmut Kirner was one of the Dornier 228 pilots contracted in the summer of 2018 to fly the permafrost mission based out of Inuvik and Yellowknife. He also flew the ferry flight back to Oberpfaffenhofen, Germany, at the end of the mission. The Dornier 228s were fitted with specialized radar equipment in Germany, and then the aircraft ferried back and forth to the Arctic. Captain Kirner recalls: “Flying over the Arctic region was quite impressive. This is an area pilots rarely get to see. The region is huge and just looking out the window as a pilot tourist it was incredible!”

Being a pilot on a research mission is extremely demanding, challenging and rewarding, and for Helmut Kirner the permafrost mission “was like seeing both sides of the mission at once; the scientific side and the pilot side.” The scientists needed absolute precision in the air, and this was “demanding but an exciting challenge for the pilots at the same time.” On this particular mission the flight crew split duties in a very unconventional way. “Teamwork was demanding and challenging. Every meter and knot had to be precise. We all had captain status. The left seat of the cockpit focused solely on the lateral track, while the right seat focused solely on altitude and speed. At the end, when the scientists told us they had obtained good research results, it was really satisfying to hear.” Before a Dornier 228 pilot can take part in such an exciting mission, they need training first. Make sure to read more in LoveDornier228’s next issue as we get an inside view into how Captain Helmut Kirner trains pilots at Simtec on their own Dornier228 simulator.

DLR project for monitoring permafrost with latest radar technology



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